Method and device for controlling the power in an asymmetric soft handover condition

ABSTRACT

A method and a device for controlling a method for controlling the power in an asymmetric soft handover condition in a communication network, including at least two cells
         each cell being served by a first type network device adapted to serve second type network devices in the respective cell. The method comprises:   temporarily adjusting (step S 3 ) a communication parameter of at least one second type network device
 
to set up and/or maintain the communication of the second type network device with the first type network device of at least one of said cells.

FIELD OF THE INVENTION

The present invention relates to a method and a device for controllingthe transmission power in an asymmetric soft handover condition in acommunication network including at least two cells.

BACKGROUND OF THE INVENTION

In mobile communication technologies like, e.g. UMTS (Universal MobileTelecommunication System), base stations—so-called first type networkdevices—serve a limited number of mobile users—so-called second typenetwork devices—according to the current location of the users. As longas a user is in a cell area of certain base station, he can obtainmobile services from that base station. The overall performance and thequality of the service depends—among others—on propagation conditions,cell type, cell size, load distribution and on the power level of thevarious signal transmissions, particularly of the pilot signal providedby each base station.

The pilot signal transmitted by each base station carries a bit sequenceor code known by the mobile stations. The bit sequence can be basestation and sector dependent. The power level of the pilot signalreceived by the mobiles is used by the mobile stations to measure therelative distance between different base stations that could be used forcommunication. Thus, the power level of the pilot signal of a basestation determines how far a mobile can “hear” the base stations; i.e.the power of the pilot signal is an indication to the mobile station ofits ability to successfully use the signal from that base station whichis transmitting that pilot signal.

In Code Division Multiple Access networks (WCDMA-Systems for example)the cell selection, re-selection and the selection of the active set ofcells which are used for communication is based on the relative strengthof the received pilot signal power (CPICH Ec/Io, wherein Ec/Io=chipenergy to total interference spectral density) from different cells.Thus, the borders of a cell are determined by the relative strength ofthe pilot signal received from different cells. Hence, the power levelof the pilot signal determines the pilot power coverage, i.e. the areaof the cell in which the pilot signal is sufficiently powered to beproperly decoded by the mobile stations.

In the CDMA-Systems tight and fast power control is an important aspect,particularly on the uplink channel to avoid that one single overpoweredmobile station blocks a whole cell. The solution is a fast closed-looppower control. By this control, the base station performs frequentestimates of the received Signal to Interference Ratio (SIR) andcompares it to a target SIR. If the measured SIR is higher than thetarget SIR, the base station will command the mobile station to lowerthe power. If it is too low, it will command the mobile station toincrease its power. The closed loop power control will thus preventpower inbalance among all the uplink signals received at the respectivebase station.

Additionally, a slower Outer Loop Power Control (OLPC-function) isprovided which adjusts the target SIR in the base station according tothe needs of the individual radio link and aims at a constant targetquality, usually defined as a bit error rate (BER) or block error rate(BLER). As one would waste much power capacity if one would set thetarget SIR to the worst case, i.e. for high mobile speeds, the targetSIR floats around a minimum value that just fulfils the required targetquality. The target SIR will change as a function of time, speed and thepropagation environment of the mobile changes. When the Outer Loop PowerControl adjusts the target SIR in the respective base station, the fastclosed loop control will react correspondingly and bring the SIR-valuereceived in the associated base stations back to the target SIR value.

During a Soft Handover situation (SHO) a mobile station is in theoverlapping cell coverage area of two cells belonging to different basestations. The communications between mobile station and the basestations take place concurrently via two air interface channels downlinkfrom each base station separately. In uplink direction, the code channelof the mobile station is received from both base stations, but thereceived data is then routed to the associated radio network controller(RNC) for combining. Then, the RNC selects the better communicationbetween the two possible radio links, and this selection takes placeperiodically, i.e. every 10 to 80 milliseconds.

In WCDMA-systems base stations are not synchronized, which is differentto other current CDMA technologies and the synchronization of a newradio link between a mobile station and the base station takes placeduring the radio link set up procedure. The uplink synchronization willbe achieved and maintained only if the base station can receive a strongenough signal from the mobile, i.e. if the transmission power of themobile station is high enough. The transmission power of the mobile, ishowever, controlled by the power control of the “stronger” radio link.In this application the stronger link is defined as radio connectionrequiring less transmission power from the mobile, and the weaker linkis defined as radio connection requiring more transmission power fromthe mobile. The “stronger” cell is defined to be the cell with thestronger link, and the “weaker” cell is defined to be the cell with theweaker link.

If the links in a soft handover area are strongly asymmetric, thetransmission power of the mobile station may not be high enough to reachthe other base station(s) where the link is weaker. This implies thatfor the cell included in the active set of cells and requiringsignificantly higher transmission power from the mobile, the uplinksynchronisation will not be achieved or maintained, and the link set upto establish a soft handover procedure or the maintaining of the softhandover will practically fail.

This applies to any communication system where the transmission of asecond type network devices (e.g. mobile) is received by more than onefirst type network device (e.g. base station) to setup and/or maintain acommunication link but its transmission power cannot be adjustedindividually to each first type network devices.

SUMMARY OF THE INVENTION

Therefore, the object underlying the invention resides in providing anenhanced method and device for controlling the power in an asymmetricsoft handover situation in a communication network.

This object is solved by a method for controlling the power in anasymmetric soft handover condition in a communication network, includingat least two cells

-   -   each cell being served by a first type network device adapted to        serve second type network devices in the respective cell,        the method comprising:    -   temporarily adjusting (step S3) a communication parameter of at        least one second type network device        to set up and/or maintain the communication of the second type        network device with the first type network device of at least        one of said cells.

The above object is also solved by a device for controlling the power inan asymmetric soft handover condition in a communication network,including at least two cells

-   -   each cell being served by a first type network device (BS1, BS2)        adapted to serve second type network devices (MS) in the        respective cell,        the device comprising:    -   additional control means for temporarily adjusting a        communication parameter of at least one second type network        device        to set up and/or maintain the communication of the second type        network device with the first type network device of at least        one of said cells.

In accordance with the invention, the communication between first andsecond type network devices can be achieved and maintained even in anarea where the cells are under strongly asymmetric conditions, and onlya relevant communication parameter, for example the transmission powerof the second type network device in question will have to be adjustedtemporarily, exactly when needed.

Preferably, the communication parameter adjusted in the adjustment stepincludes the transmission power of the second type network device inquestion, so that the first type network devices, which serve the cells,remain unchanged.

Before adjusting the communication parameter in the adjusting step,preferably, information is detected which indicates the link quality ofthe second type network device in both cells (detecting step S1), andthen an asymmetry parameter is evaluated, said asymmetry parameterindicating the imbalance of the link quality in the serving cells(evaluating step S2). On the basis of this asymmetry parameter, thetransmission power of the second type network device in question isadjusted, if the asymmetry parameter exceeds a first threshold value.

In a preferred embodiment of the invention, this object is solved by amethod for controlling the transmission power in an asymmetric softhandover condition in a mobile telecommunication network, including atleast two cells partly overlapping each other

-   -   each cell being served by a first type network device adapted to        serve second type network devices in the respective cell,    -   radio links in the stronger cell requiring less transmission        power and in the weaker cell requiring more transmission power        from the second type network device,        the method comprising the following steps:    -   detecting information (step S1), said information indicating the        radio link quality of the radio links between the second type        network device and the first type network device of the        overlapping cells    -   evaluating a asymmetry parameter in the overlapping cell area        (step S2) on the basis of the information gained in the        detecting step (S1), said asymmetry parameter indicating the        imbalance of the link quality in the overlapping cells    -   temporarily increasing (step S3) the transmission power of said        second type network device        -   if the second type network device enters the overlapping            cell area from the stronger cell and        -   if the asymmetry parameter evaluated in step S2 exceeds a            first threshold value,            to set up and/or maintain an uplink synchronization with the            first type network device of the weaker cell.

In a preferred embodiment, the above object is also solved by a devicefor controlling the transmission power in an asymmetric soft handovercondition of a mobile telecommunication network, including at least twocells (C1, C2) partly overlapping each other and participating in thesoft handover

-   -   each cell being served by a first type network device (BS1, BS2)        adapted to serve second type network devices (MS) in the        respective cell,    -   a closed loop power control means controlling the transmission        power of each second type network device in response to a        comparison of the detected SIR-data (signal to interference        ratio data) of its actual radio link, with a SIR-target value,    -   an outer loop power control means (OLPC) providing and        actualizing the SIR-target value for the closed loop power        control means,    -   radio links in the stronger cell (C1) of said cells requiring        less transmission power and radio links in the weaker cell (C2)        requiring more transmission power from the second type network        device,        the device comprising the following steps:    -   detection means for detecting information, said information        indicating the radio link quality of the radio links between the        second type network device (MS) and the first type network        device (BS1, BS2) of the overlapping stronger cell (C1) and        weaker cell (C2), respectively    -   evaluation means for evaluating a asymmetry parameter in the        overlapping cell area on the basis of the information gained        from the detecting means, said asymmetry parameter indicating        the imbalance of the link quality in the overlapping stronger        cell (C1) and weaker cell (C2),    -   additional control means for temporarily increasing the        transmission power of said second type network device        -   if the second type network device enters the overlapping            cell area from the stronger cell and        -   if the asymmetry parameter evaluated by the evaluation            means, exceeds a first threshold value,            to set up and/or maintain an uplink synchronization with the            first type network device of the weaker cell (C2).

Preferably, the link quality is represented—in accordance with theinvention—by the link power budget of the respective links.

In a soft handover situation, i.e. when a mobile station (second typenetwork device) is in the overlapping cell coverage area of two adjacentcells, the radio links of the mobile station to the base station (firsttype network device) of the “stronger” cell needs less transmissionpower from the second type network device than in a weaker cell.

If the mobile, i.e. the second type network device, is coming from thecell with the stronger link, i.e. from the cell transmitting the commonpilot channel at a comparatively high level, the method according to theinvention will establish the uplink synchronization with the first typenetwork device of the weaker cell, thus implementing the weaker link.However, the second type network is not necessarily coming from the cellwith the stronger link. If the second type network device enters fromthe cell with the weaker link into the overlapping area, thetransmission power of the second type network device according to thisinvention is temporarily prevented from being lowered by the powercontrol of the strongest link—and not increased—so as to meet theconditions required for soft handover. Otherwise, the uplinksynchronization to the first network device of the stronger cell willsucceed, but then the new stronger link will control the transmissionpower of the second type network device and the original cell'ssynchronization will fail.

To overcome these drawbacks, the invention detects informationcharacterizing the radio link imbalance in the weaker cell and in thestronger cell. This information is used to evaluate an asymmetryparameter which is a measure of the radio link imbalance between themobile and the respective base stations being different, i.e.asymmetric. The enhanced power control of the invention then increasesthe transmission power of the respective mobile station respectivelyprevents it from being lowered by the power control of the strongestlink, in order to get resp. maintain a strong enough transmission signalfor the weaker radio link to reach and maintain the uplinksynchronisation of the signal emitted by that mobile station. Thus, inaccordance with the invention the base station in the weaker cell willestablish resp. maintain the synchronisation of the mobile stationduring soft handover, when the radio link is set up.

By the invention Soft Handover—an important feature of a WCDMAsystem—will be possible in strongly asymmetric overlapping cell areas.Only the mobile station in question increases respectively does notlower due to the power control of the strongest link the power, whereasa desensitisation of the respective base station of the strongest linkwould increase the transmission power of all mobile stations in thestronger cell. As the transmission power of the mobile station inquestion increases only temporarily, i.e. exactly when needed, theinvention is economically handling the power budget. Temporary asymmetryin soft handover, e.g. due to different cell load (noise rise) will behandled automatically and no extra margin needs to be reserved therefor.

Finally, the concept of the invention allows more design freedom in thenetwork in so-called future auto tuning systems which automaticallyadjust the relative strength of received pilot power in the cells. Whenthe asymmetry in radio links in a SHO-area is not limiting the autotuning capabilities, these auto tuning features are significantly morevaluable.

In accordance with the preferred embodiment of the invention, thetransmission power of the second type network device, i.e. the mobilestation increases only, if the asymmetry parameter evaluated exceeds afirst threshold value, and if additionally the mobile station enters theoverlapping cell area, which is the soft handover area, SHO-area.Preferably, the transmission power of a respective mobile stationresumes the original value or a different value, when the mobile stationleaves the overlapping cell area. The new value of the transmissionpower may be newly determined by the power control of the serving cell.

The asymmetry parameter, indicating the different quality of radio linksin the overlapping cells is dependent on different variables or factors,among which are the CPICH power level difference, the CPICH-E_(c)/I_(o)difference, wherein E_(c)/I_(o) is the chip energy to total interferencespectral density; and the asymmetric uplink sensitivity established bymast head amplifiers if used. The different interference situation dueto different cell loads is also relevant with regard to the asymmetryparameter also, the difference in required uplink E_(b)/N_(o) may betaken into account for determining the asymmetry parameter with regardto the overlapping cells involved, E_(b)/N_(o) being the signal tointerference ratio in the radio access bearer of the radio links. One ormore of these factors or variables may be detected in accordance withthe invention to evaluate an asymmetry parameter of the invention.

In accordance with the preferred embodiment of the invention, each firsttype network device of each of the overlapping cells estimates thereceived Signal to Interference Ratio (SIR-value), i.e. for the strongercell(s) and for the weaker cell(s), this SIR-value describing the radiolink quality between the second type network device and the respectivefirst type network devices effectively and individually. To evaluate theasymmetry parameter of the overlapping cells, an offset value ΔSIR iscalculated. This offset value ΔSIR should be calculated based onmeasurements (noise rise, Eb/No) and parameters (CPICH transmit power,MHA). ΔSIR itself could be the radio link asymmetry parameter. Thecalculation will be done preferably in the network radio controller.

To enhance the control of the transmission power of the second typenetwork device the SIR-target value involved in the closed loop powercontrol of said device is adjusted in response to the asymmetryparameter. If for example the ΔSIR-value is defining the asymmetryparameter and is added as an SIR-offset value when the second typenetwork device enters the SHO-area from the stronger cell, the closedloop power control will command the second type network device toincrease its transmission power. Thus, in accordance with the invention,the SIR-target value originally provided by the outer loop power control(OLPC) is increased by a respective SIR-offset value which correspondsto the asymmetry parameter, so that the fast closed loop power control,which individually commands the transmission power of the second typenetwork device, is working on an increased target and will thus commanda correspondingly higher transmission power. The SIR-target value willresume the original value defined by the outer loop power control OLPCwhen the weaker cell, i.e. the unbalanced cell is removed from theactive set of cells, or when the asymmetry condition is no longerexisting. In case the second type network device enters the SHO areafrom the weaker cell, the transmission power of the second type networkdevice is maintained at the current level instead of increased in orderto maintain the weaker link.

Preferably, the SIR-offset value is a constant value. In accordance withan alternative embodiment of the invention, the SIR-target valueprovided by the OLPC-function is increased by adding an SIR-offsetvalue, and the resulting new SIR-target value is kept constant as longas the asymmetry condition is present, or as long as the asymmetryparameter exceeds a pre-given threshold value. In accordance with athird alternative embodiment of the invention, the minimum allowedSIR-target value is adjusted, preferably increased, to guarantee therequired transmission power of second type network device for setting upand/or maintaining all links envolved in the soft handover.

All embodiments, which increase resp. maintain the SIR-target valueprovided by the OLPC-function are based on the idea to temporarilyadjust the target value of the closed loop power control, and as thisclosed loop power control is executed at a rate of for example 1.5 kHz,this increase operates faster than any significant change of pathlosscould possibly happen. Once the asymmetry condition is over or theunbalanced, weak cell is removed from the active set of cells, theSIR-target value will resume its original value defined by the OLPCfunction and again being constantly updated by OLPC.

In the closed loop power control the respective first type networkdevice, i.e. the respective base station, performs frequent estimates ofthe received signal to interference ratio (SIR) and compares it to thetarget SIR and this first type network device will command the secondtype network device, i.e. the mobile station, to adjust the poweraccordingly. This closed loop power control is very fast (i.e. 1500times per second) and prevents any power inbalance among all the uplinksignals received in the first type network device. In this context, theOLPC-function adjusts the target SIR set point in the first type networkdevices according to the needs of the individual radio link and aims ata constant quality, usually defined as a certain target bit error rateBER or block error rate BLER. The target SIR set point will change overtime as the speed and the propagation environment of the second typenetwork device changes.

When the asymmetry parameter evaluated in the evaluation step exceeds apre-given first threshold value and thus requires temporarily increasingresp. maintaining the transmission power of the second type networkdevice located in the overlapping cell area, this adjustment will berealized—in accordance with one further preferred embodiment of theinvention—by increasing the quality target of the strongest links OuterLoop Power Control. The Outer Loop Power Control will increase resp.maintain the SIR-target value for the respective second type networkdevice which is in soft handover condition. To resume the originalSIR-offset value, the quality target is changed to its original value sothat the OLPC-function commands the SIR-target value back to theoriginal. This adjustment of the SIR-target value is determined by thereact time of the OLPC-function, and is thus somewhat slower thanchanging the SIR-target value directly. However, this embodiment of theinvention allows the SIR-target value to be fully controlled by the OLPCfunction in the radio network control of the network during theseasymmetric soft handover situations and may result in a lower SIR-targetin the first type network devices participating in the soft handover,thus reducing the uplink interference.

The invention can be implemented either by directly modifying theSIR-target value of the uplink OLPC function in the radio networkcontroller or by reducing the error rate target (e.g. BLER or BER) ofthe transport channels within the particular radio resource controlconnection (RRC connection) during the soft handover situation. In anycase, the situation is properly resumed when the unbalanced link, i.e.the unbalanced cell is moved from the active set, e.g. when the softhandover situation between unbalanced radio links belonging to differentradio link sets is over.

In accordance with the invention, modifying the SIR-target value of theuplink OLPC function may be done in two preferred ways:

-   -   increase the SIR-target value by an offset ΔSIR and keep the        increased value constant as long as the handover condition is        present resp. keep the SIR-target value constant in case the SHO        area is entered from the weakest cell;    -   increase the parameter minimum SIR-target of the uplink OLPC        function to the current SIR-target+an offset value ΔSIR resp.        maintain it, the current SIR-target being a time variable        function in this embodiment, and the offset ΔSIR being        preferably the asymmetry parameter of the invention as evaluated        in step S2.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood with reference tothe accompanying drawings in which:

FIG. 1 shows the structure of a WCDMA-network;

FIG. 2 shows a soft handover situation for a mobile station;

FIG. 3 shows a diagram representing the change of SIR-target value as afunction of time in accordance with a preferred embodiment of theinvention; and

FIG. 4 shows a diagram illustrating the change of SIR-target value as afunction of time in accordance with a second embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, preferred embodiments of the invention are describedin more detail with reference to the accompanying drawings.

According to the invention, a procedure is provided to automaticallyincrease the transmission power of a mobile station in a wideband codedivision multiple access system, if the mobile station is in a softhandover situation, said mobile being located in an area of overlappingcells.

FIG. 1 illustrates the basic structure of a WDMA-system, in which basestations BS1, BS2, BS3 each define an associated cell C1, C2, C3.Transmission links are provided from the base stations BS1, BS2, BS3 tothe Radio Network Controller RNC; data received in the base stations arerouted to the RNC for combining, for processing these data and forcontrolling the soft handover routines.

By each base station BS1, BS2, BS3 a pilot signal is emitted whichcarries a bit sequence or a code known by the mobile stations. The bitsequence is base station dependent. The received power level of thepilot signal is used by the mobile stations to measure the relativedistance between different base stations that could be used forcommunication. Thus, the power level of the pilot signal of a basestation BS1, BS2, BS3 determines the area of the associated cell C1, C2,C3. In the WCDMA-system the cell selection, re-selection and theselection of the active set of cells which are used for communication isbased on the relative strength of the received pilot powerCPICH-E_(c)/I_(o), wherein E_(c)/I_(o) is the chip energy to totalinterference spectral density from different cells. Thus, the boardersof a cell are determined by the relative strength of the received pilotsignal from the associated base station. By changing the pilot powerlevel, the area of the base station cells can be changed.

Mobile stations are in a soft handover situation SHO when the power ofthe pilot signals of two or more cells are within a predefined window.If so, the respective cells “overlap” and form the overlapping cell areaor soft handover area.

FIG. 2 illustrates soft handover for a mobile MS1 (second type networkdevice), this mobile being in the overlapping cell coverage area of thetwo cells C1 and C2 belonging to different base stations BS1, BS2 (firsttype network device). In a soft handover situation, the communicationsbetween the mobile station MS1 and the base station take placeconcurrently via two air interface channels from each base stationseparately. In downlink, the same signal is sent from BS1 and BS2 to themobile MS1 except for the power control demands. In uplink directionhowever, in soft handover the code channel of the mobile station MS1 isreceived from both base stations BS1 and BS2. The received data are thenrouted to the radio network controller RNC for further processing, andthe better radio link between the two possible connections is selectedwithin the RNC.

The uplink synchronization with the respective base station BS1, BS2will be achieved and maintained if the base station can receive a strongenough transmission signal. The transmission power however, iscontrolled by the power control of the stronger air link, i.e. by thatbase station which receives the better signal.

If the radio links in soft handover between the mobile MS1 and the basestations BS1, BS2 are strongly asymmetric, the transmission power of themobile MS1 may be high enough to reach one of the base stations, i.e.the base station of the stronger cell, it may be not high enough toreach the other base station—the base station of the weaker cell(s)—ifthe radio link is too weak. This implies, that for the significantlyweaker cell included in the active set, the uplink synchronization willnot be achieved or maintained and the radio link set up in soft handoverwill practically fail.

The invention concerns only soft handover situations in areas where theradio link power budget of the radio links to the overlapping cells areimbalanced, Different factors that contribute to the asymmetry are e.g.:

-   -   CPICH E_(c)/I_(o) difference    -   CPICH power level difference (e.g. different transmit powers in        micro and macro cells).    -   Mast head amplifier used (asymmetric uplink sensitivity).    -   Different interference situation due to different cell loads        (asymmetric noise rise).    -   Difference in required uplink E_(b)N_(o).

-   E_(b)=energy per user bit

-   N_(o)=interference and noise power density.

In accordance with the invention, the procedure to automaticallyincrease the transmission power of a mobile station MS1 in soft handoverincludes a first step in which information is detected which indicatesthe radio link power budget of the radio links to the base station BS1of cell C1 and to base station BS2 of cell C2.

In a second step, this information is used to evaluate a radio linkasymmetry parameter in the overlapping cell area. This parameterindicates the imbalance of the radio links in the overlapping strongercell and weaker cell.

In a third step, the transmission power of the mobile station MS1 istemporarily increased if the asymmetry parameter exceeds a firstthreshold value, this power increase being such that the mobile reachesthe base station of the weaker cell at a level which is sufficient toset up and maintain the uplink synchronization with the respective basestation so that the soft handover will be performed.

The transmission power of each second type network device MS1 iscontrolled in response to the detected SIR-data of its actual radiolink, these values being compared with a SIR-target provided andactualised by the OLPC-function in the Radio Network Controller.

In accordance with one embodiment of the invention the asymmetryparameter indicating the imbalance difference of the radio links in theoverlapping stronger cell and weaker cell is calculated a SIR-offsetvalue ΔSIR which is added to the SIR-target value provided by the outerloop power control at time t₁, i.e. when the second type network deviceenters the soft handover area, cf. FIG. 3. As a consequence ofincreasing the SIR-target value which is forwarded to all first typenetwork devices of the overlapping cells, the transmission power of therespective second type network devices increases simultaneously.

When the second type network device leaves the soft handover area attime t₂, the SIR-target value resumes the original value in the uplinkOLPC-function of the radio network controller RNC, cf. FIG. 3. TheSIR-target value is updated via the dedicated channel frame protocol.

As the SIR-target value is the reference value in the fast closed loopcontrol for the transmission power of each second type network device,the increase of the SIR-target value is effected in all base stationsinvolved in the soft handover. then, the closed loop power controlautomatically adjusts the transmission power of the respective secondtype network device correspondingly. By this procedure, the transmissionpower of the second type network device is increased to such a levelthat the uplink synchronisation with the first type network device, e.g.the base station of the weaker cell is set up and/or maintained as longas the asymmetric situation is present, i.e. as long as the second typenetwork device is in the overlapping cell area.

During time t₁ and t₂, i.e. when the second type network device entersand leaves the soft handover area, the SIR-target value may—in onealternative embodiment of the invention—also be kept constant during thesoft handover condition instead of showing the time dependencydetermined by the OLPC-function or assumed to be the minimum SIR-targetvalue.

FIG. 4 shows the time dependency of the SIR-target value realized in asecond embodiment of the invention. In this embodiment the invention isimplemented by increasing the quality target of the transport channelswithin the particular Radio Resource Control connection(RRC-connection), i.e. the target bit error rate BER or the target blockerror rate BLER of the respective transport channels are reduced inaccordance with the asymmetry parameter evaluated from the detectedasymmetry information.

The quality target is changed at time t₁, if the second type networkdevice MS1 enters the SHO-area, and the original value of the qualitytarget is resumed at time t₂, i.e. when the soft handover betweenunbalanced radio links belonging to different cells is over. Whenincreasing the quality target, the uplink OLPC-control function locatedin the RNC increases the SIR-target value correspondingly, this increasebeing however subject to the time constant of the OLPC-function, so thatthe SIR-target value increase is slower, cf. FIG. 4. This embodiment, ifnot too slow to cope with quick status changes, allows the SIR-targetvalue to be fully controlled by the OLPC function in the radio networkcontrol during these asymmetric soft handover situations. The solutionmay result in a lower SIR-target value in the base stationsparticipating in the soft handover, thus reducing the uplinkinterference.

1. A method for controlling the power in an asymmetric soft handovercondition, the method comprising: evaluating an asymmetry parameter inthe cell area; temporarily adjusting a communication parameter of atleast one second type network device on the basis of the asymmetryparameter to set up and/or maintain the communication of the second typenetwork device with the first type network device of at least one ofsaid cells; and controlling the power in an asymmetric soft handovercondition in the communication network, wherein the communicationnetwork includes at least two cells, each cell being served by a firsttype network device configured to serve second type network devices inthe respective cell.
 2. Method according to claim 1, wherein thecommunication parameter adjusted during the adjusting of thecommunication parameter includes the transmission power of the secondnetwork device.
 3. A method according to claim 1, the method comprising:detecting information, said information indicating the link quality ofthe links between the second type network device and the first typenetwork devices of the cells; and temporarily adjusting the transmissionpower of at least one of said second type network devices in theadjusting step if the asymmetry parameter evaluated in the evaluating anasymmetry parameter exceeds a first threshold value; wherein in theevaluating step the asymmetry parameter in the cell area is evaluatedbased on the information detected, said asymmetry parameter indicatingan imbalance of the link quality in the cells.
 4. A method according toclaim 1, wherein said at least two cells partly overlap each other, eachcell being served by a first type network device configured to servesecond type network devices in the respective cell, links in thestronger cell requiring less transmission power and in the weaker cellrequiring more transmission power from the second type network device,the method further comprising: detecting information, said informationindicating the link quality of the links between the second type networkdevice and the first type network device of the overlapping cellsevaluating an asymmetry parameter in the overlapping cell area on thebasis of the information gained in the detecting step, said asymmetryparameter indicating the imbalance of the link quality in theoverlapping cells; temporarily increasing the transmission power of saidsecond type network device in the adjusting of the communicationparameter; if the second type network devices enter the overlapping cellarea from the stronger cell; and if the asymmetry parameter evaluated inthe evaluation of the asymmetry parameter exceeds a first thresholdvalue, to set up and/or maintain an uplink synchronization of the secondtype network device with the first type network device of the weakercell.
 5. A method according to claim 4, wherein the communicationnetwork is a mobile telecommunication network.
 6. A method according toclaim 4, wherein the transmission power of the second type networkdevices are maintained in the adjusting of the communication parameter,if the second type network device enters the overlapping cell area fromthe weaker cell(s).
 7. A method according to claim 4, wherein thetransmission power of the second type network device resumes anothervalue when said second type network device leave the overlapping cellarea.
 8. A method according to claim 7, wherein the transmission powerof the second type network device resumes the original value which waspresent before entering the overlapping area.
 9. A method according toclaim 7, wherein the transmission power of the second type networkdevice resumes a value newly determined by power control of the servingcell.
 10. A method according to claim 4, wherein the link qualityinformation in the detecting step includes the link power budgetinformation.
 11. Method according to claim 4, wherein the detecting ofinformation is further adapted to include the detection of at least oneof the following values: CPICH-E_(c)/I_(o) value of the overlappingcells, CPICH power levels of the overlapping cells the uplinksensitivity of the overlapping cells, the different interferencesituation of the overlapping cells due to different cell loads, thedifference in required uplink E_(b)/N_(o), whereby E_(c)=average energyper PN chip for the pilot signal I_(o)=total received power densityincluding signal and interference E_(b)=energy per user bitN_(o)=.interference and noise power density.
 12. Method according toclaim 4, wherein the detecting of information is further adapted toinclude the detection of the SIR-data (signal to interferenceratio-data) for radio links of the second type network device with thefirst type network device of the stronger cell and the weaker cell. 13.Method according to claim 12, wherein an SIR-offset value ΔSIR iscalculated in the evaluation step on the basis of the information gainedin the detected information, the asymmetry parameter corresponding tothis SIR-offset value.
 14. Method according to claim 13, wherein thetransmission power of said second type network device increases byadding the SIR-offset value to the SIR-target value, the resulting newSIR-target value being forwarded to the first type network devices ofthe overlapping cells, the resulting new SIR-target value being keptconstant as long as the asymmetry parameter exceeds a pre-given value.15. Method according to claim 14, wherein the SIR-target of the firsttype network devices resumes the original value when the weaker cellhaving reduced radio link conditions, is removed from the active set ofcells.
 16. Method according to claim 14, wherein the SIR target of thefirst type network devices resumes the original value when the asymmetryparameter evaluated in the evaluation of the asymmetry parameterdecreases below the first threshold value.
 17. Method according to claim14, wherein the SIR-target of the first type network devices resumes theoriginal value when the second type network device leaves theoverlapping cell area.
 18. Method according to claim 14, wherein theSIR-target of the first type network devices resumes a value differentfrom the original value, when the second type network device leaves theoverlapping cell area.
 19. Method according to claim 13, wherein theSIR-offset value is a constant value.
 20. Method according to claim 13,wherein to temporarily increase the transmission power of the secondnetwork device, the Minimum SIR-target value of the uplink Outer LoopPower Control function is increased tominimum SIR-target=current SIR-target+ΔSIR, and is forwarded to thefirst type network devices of the overlapping cells.
 21. Methodaccording to claim 4, wherein the transmission power of each second typenetwork device is controlled in response to an increased SIR-targetvalue provided and actualised by an outer loop power control (OLPC) andforwarded to the first type network devices of the overlapping cells.22. Method according to claim 4, wherein the transmission power of thesecond type network device is maintained at the increased level as longas the strong radio link asymmetry evaluated in the evaluation of theasymmetry parameter exists in the overlapping cell area.
 23. Methodaccording to claim 4, wherein increasing the transmission power in theadjusting of the communication parameter includes temporarily increasingthe quality target of the Outer Loop Power Control means (OLPC function)on the basis of the asymmetry parameter gained in the evaluation of theasymmetry parameter, as a result of which the Outer Loop Power Controlmeans temporarily increases the SIR-target value for the said secondtype network device which is in soft handover condition.
 24. Methodaccording to claim 23, wherein temporarily increasing the quality targetis realized by temporarily reducing the target Bit Error Rate(BER-target) or the target Block Error Rate (BLER-target) for the cellsinvolved in handover.
 25. Method according to claim 24, resuming thequality target to the original value when the radio link asymmetryevaluation is over.
 26. Method according to claim 24, increasing thequality target of the outer loop power control when the second typenetwork device enters the overlapping cell area.
 27. Method according toclaim 4, wherein the mobile telecommunication network is a wideband codedivisional multiple access network (WCDMA-System).
 28. Method accordingto claim 1, wherein the first type network device is a base station. 29.Method according to claim 1, wherein the second type network device is amobile station.
 30. Device for controlling the power in an asymmetricsoft handover condition in a communication network, including at leasttwo cells each cell being served by a first type network device (BS1,BS2) adapted to serve second type network devices (MS) in the respectivecell, the device comprising: evaluation unit configured to evaluate anasymmetry parameter in the cell area additional control unit configuredto temporarily adjust a communication parameter of at least one secondtype network device based on the asymmetry parameter to set up and/ormaintain the communication of the second type network device with thefirst type network device of at least one of said cells, wherein poweris controlled in a communication network, including at least two cells,each cell being served by a first type network device (BS1, BS2) adaptedto serve second type network devices (MS) in the respective cell. 31.Device according to claim 30, for controlling the power in an asymmetricsoft handover condition of a communication network, including at leasttwo cells (C1, C2) partly overlapping each other and participating inthe soft handover each cell being served by a first type network device(BS1, BS2) configured to serve second type network devices (MS) in therespective cell, a closed loop power control unit configured to controlthe transmission power of each second type network device in response toa comparison of the detected SIR-data (signal to interference ratiodata) of its actual radio link, with a SIR-target value, an outer looppower control unit (OLPC) providing and actualizing the SIR-target valuefor the closed loop power control means, radio links in the strongercell (C1) of said cells requiring less transmission power and radiolinks in the weaker cell (C2) requiring more transmission power from thesecond type network device, the device further comprising: detectionunit configured to detect information, said information indicating theradio link quality of the radio links between the second type networkdevice (MS) and the first type network device (BS1, BS2) of theoverlapping stronger cell (C1) and weaker cell (C2), respectively; andadditional control unit configured to temporarily increase thetransmission power of said second type network device if the second typenetwork device enters the overlapping cell area from the stronger celland if the asymmetry parameter evaluated by the evaluation unit, exceedsa first threshold value, to set up and/or maintain an uplinksynchronization with the first type network device of the weaker cell(C2); wherein the asymmetry parameter is evaluated in the overlappingcell area by the evaluation unit based on the basis of the informationdetected by the detecting unit, said asymmetry parameter indicating animbalance of the link quality in the overlapping stronger cell (C1) andweaker cell (C2).
 32. Device according to claim 31, wherein the linkquality information gained by the detection unit includes link powerbudget information.
 33. Device according to claim 31, wherein theadditional control unit is further configured to temporarily maintainsthe transmission power of said second type network device, if the secondtype network device enters the overlapping cell area from the weakercell.
 34. Device according to claim 31, wherein the additional controlunits is further configured to increase the transmission power of thesecond type network device (MS) is incorporated in the closed loop powercontrol means and/or the outer loop power control unit (OLPC). 35.Device according to claim 31, wherein the additional control unitincreases the transmission power of said second type network device (MS)only when the second type network device enters the overlapping cellarea.
 36. Device according to claim 31, wherein the additional controlunit resumes the original value of the transmission power of said secondtype network device when said device leaves the overlapping cell area.37. Device according to claim 31, wherein the transmission power of thesecond type network device resumes a value newly determined by the powercontrol unit of the serving cell, when said second type network deviceleaves the overlapping cell area.
 38. Device according to claim 37,wherein the additional control unit resumes the SIR-target value of thefirst type network devices to the original value when the second typenetwork device leaves the overlapping cell area.
 39. Device according toclaim 31, wherein the detection unit is further configured to includethe detection of at least one of the following values: CPICH-E_(c)/I_(o)value of the overlapping cells, CPICH power level difference of theoverlapping cells, the uplink sensitivity of the overlapping cells, thedifferent interference situation of the overlapping cells due todifferent cell loads, the difference in required uplink E_(b)/N_(o),whereby E_(o)=average energy per PN chip for the pilot signalI_(o)=total received power density including signal and interferenceE_(b)=energy per user bit N_(o)=. interference and noise power density.40. Device according to claim 31, wherein the detecting unit isconfigured to include the detection of the SIR-data (signal tointerference ratio-data) for radio links of the second type networkdevice (MS) with the first type network device (BS1, BS2) of thestronger cell (C1) and the weaker cell (C2).
 41. Device according toclaim 31, wherein the evaluation unit calculates an SIR-offset valueΔSIR on the basis of the information received by the detection unit, theasymmetry parameter corresponding to this SIR offset value.
 42. Deviceaccording to claim 40, wherein the SIR-offset value is a constant value.43. Device according to claim 31, wherein an additional control unitadds the SIR-offset value ΔSIR to the SIR-target value provided by theouter loop power control (OLPC) and forwards this new SIR-target valueto the fist type network devices of the overlapping cells.
 44. Deviceaccording to claim 31, wherein an additional control unit adds theSIR-offset value ΔSIR to the actual SIR-target value when the secondtype network device enters the overlapping area and keeps the resultingnew SIR-target value constant as long as the asymmetry parameter exceedsa pre-given value.
 45. Device according to claim 31, wherein totemporarily increase the transmission power of the second network deviceby the additional control unit, the minimum SIR-target value of theuplink OLPC function in the radio network controller will be increasedtominimum SIR-target=current SIR-target+ΔSIR, and is forwarded to thefirst type network device of the overlapping cells.
 46. Device accordingto claim 31, wherein the SIR-target value of the first type networkdevices (BS1, BS2) resumes the original value when the weaker cell (C2)having reduced radio link conditions, is removed from the active set ofcells.
 47. Device according to claim 31, wherein the SIR-target value ofthe first type network devices (BS1, BS2) resumes a value different fromthe original value, when the weaker cell (C2) having reduced radio linkconditions, is removed from the active set of cells.
 48. Deviceaccording to claim 31, wherein the additional control unit resumes theSIR target value of the first type network devices to the original valuewhen the radio link asymmetry evaluated in the evaluation unit decreasesbelow the first threshold value.
 49. Device according to claim 48,wherein the additional control unit resumes the quality target to theoriginal value when the radio link asymmetry is over.
 50. Deviceaccording to claim 31, wherein the additional control unit resumes theSIR-target value of the first type network devices to the original valuewhen the radio link asymmetry decreases below a second threshold valuewhich is smaller than the first threshold value.
 51. Device according toclaim 31, wherein the additional control unit is incorporated in theouter loop power control means (OLPC) and/or the closed control unit andincreases temporarily the quality target of the outer loop power controlunit (OLPC function) on the basis of the asymmetry parameter receivedfrom the evaluation unit, as a result of which the outer loop powercontrol unit automatically increases the SIR-target value for the saidsecond type network device which is in soft handover condition. 52.Device according to claim 51, wherein temporarily increasing the qualitytarget is realized by temporarily reducing the target Bit Error Rate(BER-target) or the target Block Error Rate (BLER-target) for the cellsinvolved in handover.
 53. Device according to claim 31, wherein theadditional control unit increases the quality target of the outer looppower control unit when the second type network device enters theoverlapping cell area.
 54. Device according to claim 31, wherein thefirst type network device (BS1, BS2) is a base station.
 55. Deviceaccording to claim 31, wherein the second type network device (MS) is amobile station.
 56. Device according to claim 31, wherein the closedloop power control unit is arranged in the first type network devices(BS1, BS2) and wherein the outer loop power control unit (OLPC) isarranged in the Radio Network Controller (RNC) of the first type networkdevices (BS1, BS2).
 57. Device according to claim 31, wherein thecommunication network is a mobile telecommunication network.
 58. Deviceaccording to claim 31, wherein the mobile telecommunication network is aWideband Code Division Multiple Access Network (WCDMA System).